Application of Diversity Techniques for Multi User IDMA Communication System

In wireless communication, fading problem is mitigated with help of diversity techniques. This paper presents Maximal Ratio Combining (MRC) diversity approach to uproot the fading problem in interleave-division multiple-access (IDMA) scheme. The approach explains receiver diversity as well as transmits diversity analysis as 1:2 and 2:1 antenna system in fading environment, no. of antennas can be increased to improve diversity order. Random interleaver as well tree based interleaver has been taken for study. Significant improvements in performance of IDMA communication is observed with application of diversity techniques. Keywords: Random Interleaver, Tree Based Interleaver, MRC diversity, IDM

A Novel Power Allocation Scheme for Two-User GMAC with Finite Input Constellations

Constellation Constrained (CC) capacity regions of two-user Gaussian Multiple Access Channels (GMAC) have been recently reported, wherein an appropriate angle of rotation between the constellations of the two users is shown to enlarge the CC capacity region. We refer to such a scheme as the Constellation Rotation (CR) scheme. In this paper, we propose a novel scheme called the Constellation Power Allocation (CPA) scheme, wherein the instantaneous transmit power of the two users are varied by maintaining their average power constraints. We show that the CPA scheme offers CC sum capacities equal (at low SNR values) or close (at high SNR values) to those offered by the CR scheme with reduced decoding complexity for QAM constellations. We study the robustness of the CPA scheme for random phase offsets in the channel and unequal average power constraints for the two users. With random phase offsets in the channel, we show that the CC sum capacity offered by the CPA scheme is more than the CR scheme at high SNR values. With unequal average power constraints, we show that the CPA scheme provides maximum gain when the power levels are close, and the advantage diminishes with the increase in the power difference.Comment: To appear in IEEE Transactions on Wireless Communications, 10 pages and 7 figure

Iterative multi-user detection of trellis code multiple access using a posteriori probabilities

Iterative detectors for trellis code multiple access (TCMA) aresuggested as an alternative to the joint maximum likelihood sequence detector(MLSD). Interleavers are introduced in the TCMA system as a newfeature to separate the users. This implies that MLSD is now too complexto implement. The conventional interference cancellation (IC) detector haslower complexity, but its performance is shown to be far from acceptable.Another iterative detector having close to single user performance is thereforesuggested. Instead of using IC, this detector updates the branch metricfor every iteration and avoids the standard Gaussian approximation. It isalso shown that the users can be detected when the interleaver is the onlyuser specific feature in the TCMA system

Iterative multi-user detection of trellis code multiple access using a posteriori probabilities

Iterative detectors for trellis code multiple access (TCMA) aresuggested as an alternative to the joint maximum likelihood sequence detector(MLSD). Interleavers are introduced in the TCMA system as a newfeature to separate the users. This implies that MLSD is now too complexto implement. The conventional interference cancellation (IC) detector haslower complexity, but its performance is shown to be far from acceptable.Another iterative detector having close to single user performance is thereforesuggested. Instead of using IC, this detector updates the branch metricfor every iteration and avoids the standard Gaussian approximation. It isalso shown that the users can be detected when the interleaver is the onlyuser specific feature in the TCMA system